Healthy Brain, Happy Life (26 page)

With chronic activation of the sympathetic system, you get all your emergency systems active all the time: Your heart rate is a little higher, your blood pressure is always elevated, and your blood glucose level is at a constant high, making less blood available for digestion and reproduction. It is easy to see how chronic sympathetic nervous system activation can lead to heart disease, diabetes, ulcers, and long-term reproductive problems such as erectile dysfunction and disruption of menstrual cycles. Not only that, but long-term stress weakens our immune systems, making us more susceptible to disease and prolonging recovery from injury. So while our built-in stress-response system is beautifully adapted to react to unforeseen acute dangers, it turns on us when chronic stress invades our lives.

And the bad news gets even worse. Long-term chronic stress negatively affects the brain. A long and rich history in neuroscience research has focused on these negative effects of long-term stress and, in particular, high levels of cortisol on brain function, and the story is not good. The three major brain areas affected by long-term stress are the hippocampus, the prefrontal cortex and the amygdala, which are the centers for memory, executive function, and managing emotion. Sound important? You bet.

The hippocampus is particularly vulnerable to stress because hippocampal cells are endowed with the largest number of cortisol receptors in the brain. A receptor is like a specialized doorway into a cell that allows particular hormones or neurotransmitters to modulate the inner working of the cell in a range of ways. As a consequence of all those cortisol receptors, hippocampal cells are highly responsive to any change in the body’s cortisol levels. With a short exposure to cortisol, hippocampal cells work better and memory is enhanced (as in the pop quiz example I gave at the beginning of the chapter). But there is strong evidence that prolonged exposure to high levels of cortisol working through those cortisol receptors damages hippocampal cells and actually accelerates the aging process by damaging proteins and other metabolic machinery in brain cells. If you artificially increase the level of cortisol in the hippocampus in rodents, you impair the animals’ physiological responses and cause shrinkage of the tree-branch-like dendrites (the input structures) of their hippocampal neurons. If the cortisol levels remain high for a long time, the hormone will actually start to kill hippocampal neurons, shrinking the overall size of the hippocampus. For this reason, long-term stress also significantly impairs long-term memory function. This is consistent with findings in humans who have endured long-term stress. For example patients with post-traumatic stress disorder (PTSD) or depression (specific conditions that are both strongly associated with long-term stress exposure) have significantly shrunken hippocampi and impaired learning and memory function, which suggest that long-term cortisol exposure has killed their hippocampal cells.

Many studies in rodents have shown that long-term stress also decreases normal hippocampal neurogenesis. When this happens, the normal infusion of new hippocampal cells starts to slow down with chronic stress. No more new brain cells! Stress will also decrease the synthesis of the growth hormone BDNF. Because BDNF is critical for the growth and maturation of the new hippocampal cells, less BDNF also means decreased survival of any hippocampal cells that do manage to be born.

Although the hippocampus has the largest number of cortisol receptors in the brain, the prefrontal cortex is highly sensitive to even short bursts of stress. As I’ve mentioned before, the prefrontal cortex, situated just behind the forehead, is essential for some of our highest-order cognitive abilities, including working memory (defined as the memory we use to keep things in mind, also referred to scratchpad memory), decision making and planning, and flexible thinking. Studies in animals have shown even relatively mild stress can impair performance of working memory tasks that depend on the frontal lobe. Physiology studies have shown that stress not only impairs the physiological responses and functions of the prefrontal cortex but also can quickly start to damage the dendritic branches of those cells.

The third key brain area affected by long-term stress is the amygdala, which is important for emotion and, in particular, for learning about aversive stimuli. Unlike the hippocampus and prefrontal cortex that are damaged with stress, increased stress in PTSD patients works to put the amygdala into overdrive such that scientists see increased amygdala activation in PTSD patients along with inhibited prefrontal function. In particular, the region of the prefrontal cortex that exerts inhibitory control over the amygdala is the region that has been shown to be underactive in PTSD. What does this mean? That PTSD makes people more easily aroused or reactive and impairs their executive functioning, including working memory and the ability to manage emotions.

WHAT STRESSES US OUT

Like everybody else, I’ve experienced a wide range of different kinds of stress throughout my life. Early on there was just baby stress. For me it was the end of summer vacation stress that happened every year. My poor mother would have to contend with a crying child who she knew enjoyed school but who could not let go of summertime fun. The stress escalated with the SATs, college finals, and graduate school applications. However, it wasn’t until those last six months of my doctoral dissertation, leading up to my actual dissertation defense that I truly experienced my first major stressful event. This was hard. It was the moment of truth. After five and a half years of data gathering this was the moment when I had to synthesize all that data and finally see if I had something coherent, intelligent, and deep to say about all my work. The writing shouldn’t have been so difficult—I knew what all the results were—but it was those pressures to be brilliant that made the task extra hard, that made me worry my conclusions would not be as earth shattering as I hoped that they would be.

To make matters worse, I had descended into a fast-food habit. To be specific, I became a huge fan of the Jack in the Box curly fries and a burger for dinner and there was no way I was going to make time to exercise. The icing on top of my homemade stress cake was that all the stress I was putting on myself was making it very difficult to sleep. I was staying up late every night to do as much as I could, and I was exhausted, yet I never felt like I got a good night’s sleep because just as I was laying my head down on the pillow, the thought would pop into my head, Did I write enough today? That question would immediately lead to, Was the chapter I wrote good enough? and then, Will I be able to get enough done tomorrow?

Of course, you don’t have to write a dissertation to experience this kind of stress. We all experience it: losing one’s job, getting a divorce, having a health scare, worrying about money. These stressful experiences upset not only our daily routines but our ability to bounce back.

You will recognize that these are all examples of psychological stress. One of the worst things about psychological stress is that because it represents worry about what
could
happen, anything at all could become a form of psychological stress. And it never ends—it can become a vicious circle, as it did for me during that last half year of finishing my dissertation.

Situations that cause us psychological stress typically have four major characteristics. Psychological stress develops in situations in which you feel you have no control. Check! In my case, my fate was to be determined by my dissertation committee, and I felt I had no control over their judgments. It also develops in situations in which you have little or no predictive information; in other words, when we are faced with a big unknown. Check again! I received the okay to write my dissertation, but for much of the time of writing it, I had little feedback about its direction and had no idea of whether I was on the right path, leaving me to worry and wonder constantly about where I stood.

Psychological stress gets worse in situations in which we have no outlets for our stress. You may recall that at this time in my life, I barely had a social life. I had effectively taken my major outlets (hobbies, such as playing music) away from myself in the name of working hard. I did not give myself time to exercise or eat well or even sleep very well, and it would have been out of the question to spend time on frivolous pursuits, such as relaxing and going to the movies or dinner with friends.

The last situation that feeds the psychological stress monster is the feeling that things are getting worse. Even though I knew there was light at the end of the tunnel (that I
would
have to turn in my dissertation), I still couldn’t get myself to believe that things were going to work out. I was so stuck in stress mode, it felt impossible to do the mental reality check that would have reassured me:
Wendy, it’s going to be all right. You’ve worked years on this, you know your stuff.
No, this positive self-talk was not happening then.

Even if you haven’t written a dissertation, I am sure you can relate to this story: a period of time when you felt besieged by stress. Maybe it’s waiting for a house to be sold or preparing for a move or applying to school (for you or your child!). The good news is that we can use our brains to help ourselves manage these stressors. In fact, many stress-management strategies try to reverse or diminish the four major aspects of psychological stress. For example, in situations in which you feel you have no control, figure out where you
can
take control of the situation to enhance your feeling of personal power. If you feel you have no predictive information, try to ask more questions to get the information you need to address the problem. Are you worried about how you are doing at work, or do you think your boss or colleagues are speaking badly about you? Figure out a way to get some feedback so you can do a reality check. Taking control of even a small part of the situation can do wonders to relieve or at least diminish psychological stress.

Another big area of stress management revolves around enhancing your outlets for stress. Turn to your friends to help relieve stress or make new ones who will. Find hobbies that you enjoy that can transport you to your own personal happy place. It could be cooking, eating, walking outside in nature, or spending time with your pet—whatever works for you. And it will not be a surprise to learn that many stress-management programs emphasize both regular exercise and meditation, which many studies have shown can decrease stress and enhance your mood and feelings of well-being (as you will see in Chapter 10).

An important key is to do the exercise and meditation on a regular basis. You have to make it as much a part of your routine as the psychological stresses that you are battling for these stress-management techniques to be able to do the trick. The key is to find something that you enjoy (or you can learn to enjoy) as your stress-management solution, and you can decrease the stress and increase the happiness in your life.

 SOURCES OF STRESS: RELATIONSHIPS

Maybe one of the most common chronic stressors in our lives (the kind that makes us sitting ducks) comes from difficult interactions with other people. Do you feel any anxiety around your parents or siblings? Does it get worse around the holidays? What about people at work? I had just such a stressful situation with a student in my lab where I didn’t even realize how much stress it was causing in my life over many months until I was able to resolve it. When this student first joined the lab, there was an initial honeymoon phase when hopes and expectations were high on both sides. But then as our personality issues clashed (him: a mixture of frenetic and laid-back energy, me: thoroughly type A), those high hopes and expectations gradually withered away, and I ended up in denial about how bad the relationship was. He was smart, but from my perspective just didn’t do the experiments I asked him to do within the time frames I asked him to do them in; he seemed to prefer to do things his own way and at his own pace. I found him petulant and generally unproductive, and I’m sure he found me demanding and overbearing. It got so bad that I simply tried to avoid the guy whenever I really didn’t have to see him. I thought I was decreasing the stress with my brilliant avoidance/denial strategy, but I was just making it worse.

Only when I was finally able to fix this broken relationship through another “doorman conversation” (see Chapter 5) did I realize just how stressful that daily interaction was on me. I remember I was even more nervous about this conversation than I had been about the one with my doorman because the last thing I wanted to do was make this work relationship even worse than it was. The thing that convinced me to actually have this conversation was my realization that as head of the lab, I was responsible for defining the kinds of relationships I wanted in my workplace. And this was definitely not one of them. I knew I needed to change it.

So I brought him into my office, sat him down, and said, “The fact is, our relationship has not been good for some time.” Surprisingly it was a huge relief to admit that out loud.